Waveguides are used in optical communication networks for the transmission and routing of optical signals. For the transmission of the optical signals over long distances, waveguides can take the form of optical fibers, thin strands of glass that are used to transfer data over distances that can span tens of kilometers. Within the networks of long range optical fibers are signal processing nodes that contain packaged photonic and optoelectronic circuits that are used to perform various functions such as to encode, send, receive, decode, multiplex, and de-multiplex, among other optical and electrical signal processing functions, the optical signals that are delivered to these processing nodes via the optical fibers. And within the optoelectronic circuits in these processing nodes, optical signals are transmitted via free space and through short lengths of waveguide. These short lengths of waveguide are used to guide signals to a variety of small packaged devices or components that can transfer, combine, split, and route optical signals as the demands of the network require.
Optoelectronic packages at signal processing nodes in optical communications networks generally include an optical submount assembly, which typically consists of one or more optical die (such as lasers and photodetectors), and that can include either the means for the free space transmission of optical signals or the planar waveguides and associated optical routing components, all of which are enclosed in an hermetically-sealed cavity formed by a cap and a substrate. A submount assembly can include, for example. a substrate or interposer, the optical routing components, and the signal-generating and signal-receiving devices and components.
Routing of optical signals from the optical fibers to components on the submount assembly have historically been accomplished via transmission in free space, and to some extent, via planar optical waveguides on the submount assembly. Optical transmission in free space can require lenses to focus and direct the optical signals between components in the optical circuits and can require large spatial volumes to accommodate these lenses. The large spatial volumes can lead to undesirably large package sizes for these optical circuits. Additionally, the transmission of the signals in free space can result in significant signal losses from uncontrolled scattering and reflection.
Currently, the capability for fabricating planar waveguide structures of sufficient thickness with low stress is limited, and therefore, a need exists in the art of optoelectronic packaging for a planar waveguide structure that can be deposited onto a substrate, and from which compact and economical interposers and submount assemblies can be formed. Thus, there is a need in the art for a method to produce compact, planar optical waveguide structures that exhibit low optical loss without deformation of the underlying substrate.